Herpes simplex virus 2 (HSV-2) is a common human pathogen that causes recurrent genital lesions in adults and disseminated disease in newborns. The virus encodes a protein kinase, UL13, which is clearly important in the virus lifecycle because UL13-deficient mutants are profoundly attenuated in mouse models of infection. Few substrates of UL13 have been identified, although the UL13 kinase activity has been linked to important cellular events such as regulation of mitosis and dissolution of the nuclear lamin network, and to modification of viral proteins that promote late gene expression. We seek to identify the consensus motif recognized by UL13 because this would greatly facilitate investigation of these important UL13-mediated processes. One report suggests that the HSV-1 UL13 utilizes the motif S/TPx[R/K/H] that overlaps the cdc2 kinase recognition motif, but our preliminary data suggest that HSV-2 UL13 recognizes a broader definition of the cdc2 motif, or instead may be equivalent to the ERK1/2 kinase recognition motif PxS/TP. We hypothesize that the HSV-2 UL13 kinase phosphorylates proteins on serine or threonine residues in the motif S/TPx[R/K/H/D] or PxS/TP. In Aim 1, we will use an in vitro kinase assay to identify the HSV-2 UL13 recognition motif through 1) mutational analyses of critical motif residues in the putative UL13 autophosphorylation site and in a potential exogenous substrate, and 2) phosphorylation of synthetic peptides encompassing each motif. In Aim 2, we will screen potential viral targets of UL13 kinase activity using 1) synthetic peptides, and 2) expressed target proteins to identify novel viral targets of UL13. Our long-range goal is to use the novel viral targets identified through application of the UL13 recognition motif to elucidate the mechanisms by which UL13 regulates viral replication and pathology. [unreadable] [unreadable]